This invention relates to prosthetic devices, and particularly a prosthetic knee, for providing an articulated joint between bones in the human or animal anatomy.
A prosthetic knee joint conventionally includes a femoral prosthesis having a condyloid portion and a fixation shank. The condyloid portion typically includes laterally spaced apart elements simulating the human knee condyles. In this type of device, the tibial prosthesis includes a weight-bearing portion stimulating the plateau of the tibia of the human knee as well as a fixation shank. The condyloid elements of the femoral prosthesis are supported by non-metallic weight-bearing portions of the tibial prosthesis. A conventional prosthetic knee may also include a shaft between the femoral and tibial prosthesis which is load or weight-bearing. This shaft is normally mounted in non-metallic bearing members non-rotatably mounted relative to the condyloid elements of the femoral prosthesis. As the shaft rotates, the non-metallic bearing members adjacent to the shaft are slowly worn away. At the same time, the non-metallic bearing surfaces of the weight-bearing portion of the tibial prosthesis which support the condyloid elements of the femoral prosthesis are also worn away. This wear results in eccentricity in the initially concentric bearing system, namely, the center of rotation of the condyloid elements deviates from the center of rotation of the shaft. Consequently, the prosthetic knee over a period of time will cease to function properly in that wear will create a distortion in the bearing geometry which will increase local bearing unit loads and thus result in an increased rate of wear, and increased eccentricity.
The device of this invention overcomes the disadvantages of the prior art devices described above by providing a prosthetic device, and particularly a prosthetic knee joint, in which all of the bearing surfaces associated with the femoral prosthesis are on the one single component of the femoral prosthesis so that the normal wear which is associated with these bearing surfaces does not change the relative centers of the rotating surfaces and thereby does not introduce eccentricity in the concentric bearing system. In addition those surfaces associated with the tibial prosthesis which are in loaded moving contact with the four bearing surfaces associated with the femoral prosthesis are of like material in order to have like wearing characteristics. With this arrangement, the prosthetic device will continue to function correctly and to simulate the normal action of the human knee irrespective of wear.
Accordingly, it is an object of this invention to provide an improved prosthetic device such as a prosthetic knee which is capable of functioning smoothly and efficiently under the normal wear involved after implantation.
It is another object of this invention to provide a prosthetic device having a femoral prosthesis defining laterally spaced apart elements simulating the human knee condyles which have first bearing surfaces defined by the outer periphery of the elements and second bearing surfaces defined by openings in the elements which are adapted to receive a weight-bearing shaft.
It is yet another object of this invention to provide a prosthetic device in which the weight-bearing shaft of the prosthesis carries low-friction bearing sleeves which rotate therewith and bear against bearing surfaces defined in the femoral prosthesis.
These and other objects of the invention, as well as many of the attendant advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.